1. Field of the Invention
The present invention relates to bleach promoting particles suitable for incorporation into detergent formulations.
2. The Related Art
Hydroperoxide generating compounds have long been known for their capability of removing stains from fabrics. Among the most commonly employed materials for this purpose is sodium perborate, either in the tetrahydrate or monohydrate form.
When laundering fabrics at or near the boil temperatures of 85.degree. C. to 100.degree. C., perborate and similar persalt materials perform well. Over the years, the temperatures at which consumers launder have, however, declined. Today it is common to conduct the washing process below 60.degree. C. Under such conditions, the speed of active oxygen release from perborate and like materials is poor. To overcome the low temperature problem, bleach precursors, alternately known as promoters or activators, have been used in conjunction with the persalts.
The literature has documented a great number of materials that function effectively as bleach precursors. One of the earliest disclosures is found in U.S. Pat. No. 3,256,198 (Matzner) revealing C.sub.6 -C.sub.10 alkyl sulphophenyl carbonates. Shorter chain carbonates have been reported in U.S. Pat. No. 3,272,750 (Chase). Other early patents in this area include GB 836,988 (Davies et al) and GB 864,798 (Hampson et al) reporting the use of aliphatic carboxylic acid esters as adjuncts for accelerating the bleach activity of persalts such as sodium perborate or percarbonate. Illustrative of esters mentioned therein are sodium acetoxybenzene sulphonate (SABS) and sodium benzoyloxybenzene sulphonate (SBOBS).
More recently in U.S. Pat. No. 4,412,934 (Chung et al), there was reported bleach precursors of the general formula RCOL where R is an alkyl group containing from 5 to 18 carbon atoms and L is a leaving group. Sodium nonanoyloxybenzene sulphonate (SNOBS) was identified therein as a particularly effective compound.
Further reports of ester precursors may be found in the following literature: U.S. Pat. No. 4,283,301 (Diehl); U.S. Pat. No. 4,536,314 (Hardy et al)); U.S. Pat. No. 3,686,127 (Boldingh et al); EP 0 106 584 (Hartman); EP 0 136 331 (Burns et al); EP 0 185 522 (Fong et al); EP 0 153 322 (Moyne et al); EP 0 153 223 (Moyne et al); and EP 0 202 698 (Nollet et al).
There also have been reported through U.S. Pat. No. 4,751,015 (Humphreys et al) a class of precursor compounds identified as quaternary ammonium or phosphonium substituted carbonic acid esters. Related quaternary ammonium carboxylic esters have been reported in U.S. Pat. No. 4,397,757 (Bright et al).
To a greater or lesser extent, all of the known bleach precursor compounds have problems with hydrolytic stability. Considerable work has been reported on efforts to combat the problem. U.S. Pat. No. 4,087,369 (Wevers) reports improving the storage stability of certain types of perbleach activator (precursor) through agglomeration with an agent that is chemically inert relative to the activator. Agglomerating agents suitable for use therein are generically described as having melting points in the range from about 25.degree. C. to 100.degree. C. Specific classes include ethoxylated C.sub.10 -C.sub.18 carboxylic acids, C.sub.10 -C.sub.15 amides, polyethylene glycols, ethoxylated C.sub.8 -C.sub.18 alkyl phenols, C.sub.12 -C.sub.30 fatty acids and C.sub.16 -C.sub.30 fatty alcohols.
U.S. Pat. No. 4,009,113 (Green et al) discloses a slightly different manner of protecting precursor compounds of the type listed by Wevers. Finely divided particulate precursor compound is evenly mixed with an inert carrier material. Around the resultant particle is placed an outer protective, non-deliquescent coherent layer of polyvinyl alcohol, polyacrylamide, copolymers of acrylic acid, methacrylic acid or maleic anhydride, starch and its modifications and derivatives (e.g. dextrins), water-soluble cellulose ether or water-soluble gum. Dextrin and sucrose are noted as preferred. A plasticizer may be incorporated within the outer protective layer. Typical plasticizers mentioned are urea, glycerol, ethylene glycol and esters of dibasic acids.
U.S. Pat. No. 3,925,234 (Hachmann et al) focuses upon stabilizing bleaching assistants of the N-acyl and O-acyl compound variety. Chief among these compounds is tetraacetyl glycoluril. Stabilization is accomplished by surrounding the bleaching assistant with another coating that is a mixture of C.sub.12 -C.sub.24 fatty acid with fatty alcohols (or water-soluble ethoxylated derivatives thereof) in a weight proportion of 10:1 to 2:1.
U.S. Pat. No. 3,833,506 (Fries et al) is concerned with the same bleaching assistants as those of Hachmann et al. Stabilization is here accomplished by forming an intimate mixture between 10-70% of a bleaching assistant and 30-90% mixture of fatty acids and polyethylene glycol.
U.S. Pat. No. 4,678,594 (Parfomak et al) encapsulates a mixture of sodium nonanoyloxybenzene sulfonate (SNOBS) and sodium perborate in a matrix of nonionic ethoxylated alcohol surfactant. Use of ethoxylated nonionic surfactant as a storage stability and water-dispersibility aid for peroxy acid bleach presursors is also reported in U.S. Pat. No. 4,399,049 (Gray et al).
Other patents directed toward solving storage stability and/or dispersibility problems for bleach presursors include U.S. Pat. No. 4,444,674 (Gray), U.S. Pat. No. 4,111,826 (Leigh et al), and U.S. Pat. No. 4,372,868 (Saran et al).
U.S. Pat. No. 4,486,327 (Murphy et al) focuses upon branched alpha-substituted derivatives of C.sub.6 -C.sub.18 carboxylic acid esters. Better storage stability of the activator is achieved by evenly distributing therewith a binder material which may be selected from nonionic surfactants, polyethylene glycols, anionic surfactants, film-forming polymers, fatty acids and mixtures thereof. Among the film-forming homo- and copolymers reported are those that include monomers selected from acrylic acid, methacrylic acid and maleic anhydride, with preference given to sodium polyacrylate.
While a great number of binder systems have been proposed, the systems often do not provide sufficiently swift solubility in water so as to timely deliver the peracid.
Another problem has been in the area of attrition resistance. Particles of binder and precursor must be sufficiently robust to withstand physical disintegration into smaller particle sizes when being blended with other particles such as detergent base powders.
Dustiness is a problem arising in large measure from low attrition resistance. Not only does dust present an explosion hazard, but long-term inhalation exposure by plant workers can lead to adverse health effects.
Accordingly, it is an object of the present invention to provide bleach precursor particles that exhibit improved water solubility and excellent water dispersibility in a wash medium.
Another object of the present invention is to provide bleach presursor particles of improved attrition resistance.
A further object of the present invention is to provide bleach precursor particles of low dustiness.
A still further objective of the present invention is to provide a detergent composition containing the bleach precursor particle which will deliver a high level of cleaning performance against stains.
These and other objects of the invention will become more apparent through the following detailed description.